Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $169.58   9.136%   $185.0728   $185.07   $185.05   $185.10  
  Purchase #2 $157.55   3.276%   $162.7113   $162.71   $162.70   $162.70  
  Purchase #3 $76.71   9.625%   $84.0933   $84.09   $84.10   $84.10  
  Purchase #4 $238.96   6.163%   $253.6871   $253.69   $253.70   $253.70  
  Purchase #5 $103.42   4.182%   $107.745   $107.75   $107.75   $107.70  
  Purchase #6 $54.50   13.703%   $61.9681   $61.97   $61.95   $62.00  
  Purchase #7 $141.27   7.500%   $151.8653   $151.87   $151.85   $151.90  
  7 purchase totals = $941.99       $1,007.1429   $1,007.15   $1,007.10   $1,007.20